<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>封装ajax</title>
</head>

<body>

</body>
<script>
    function ajax(url) {
        return new Promise((resolve, reject) => {
            let xhr = new XMLHttpRequest()
            xhr.open('get', url)
            xhr.send()
            xhr.onreadystatechange = function () {
                console.log(xhr)
                if (xhr.readyState == 4) {
                    if (xhr.status >= 200 && xhr.status < 300) {
                        let res = JSON.parse(xhr.responseText) //从后台获取js字符串，然后通过JSON.parse函数转换成json对象
                        resolve(res)
                    } else {
                        reject(xhr.responseText)
                    }
                }
            }

        })
    }
    ajax('./01.json').then((res)=>{
        console.log(res)
    })
    .catch((error)=>{
        console.log(error);
    })


</script>

</html>